Method of operating a thrust propellant motor using amalgam coated metal particles



AMALGAM J1me 1967 D. K. KUEHL ETAL METHOD OF OPERATING A THRUSTPROPELLANT MOTOR USING COATED METAL PARTICLES Filed June 29, 1964 44mmwmnmmwmm OOO OO O O comm fl/ ooQ 08m 83 1 0mm 7 OF 7 A xdwo Comm mzmh 83H o W m M W o8" n// ////67// Z? 2/ INVENTORS DONALD K. KUEHL IRVINGLASSMAN BY MORGAN,FINNEGAN,DURHAM 8| PINE ATTORNEYS United StatesPatent M Delaware Filed June 29, 1964, Ser. No. 378,604 18 Claims. (Cl.60-219) This invention relates to metal ignition and more particularlyto improving the rate and lowering the temperature of ignition of metalson which protective oxide coatings tend to form when the surface thereofis contacted with oxygen and/ or oxygen-containing environments.

This invention is particularly directed to fuels or fuel systemscomprising or utilizing metals of the type described as a component.

Metal containing fuels made in accordance with the teachings containedherein are capable of use in a wide variety of transportation andmilitary equipment. They are especially useful as high energypropellants for reaction thrust propellant motors or engines, such asmissile, rocket, jet, and ram-jet engines. In motors or engines of thetype described, fuel is burned in a combustion chamber and the productsof combustion are allowed to escape through a jet, thereby producing adriving force.

An object of this invention is to improve the rate and temperature ofignition of metals on which protective oxide coatings form when thesurface thereof is contacted with oxygen and/or oxygen-containingenvironments, i.e., oxygen containing gases, liquids, or solids, andincludes improving the rate and temperature of ignition of compositionscontaining such metals.

Another object of this invention is to improve the efficiency ofcombustion of metals of the type described, including compositionscontaining such metals.

It is another object of the present invention to provide improved metaladditives for solid, liquid and/ or hybrid rocket propellants.

Another object of the present invention is to increase the deliveredperformance of metal containing propellants by reducing ignition delay.

Another object of this invention is to provide more complete combustionof metal containing fuels in combustion chambers of thrust propellantengines.

Still another object of the present invention is to provide surfaceactivated metal particles which may be incorporated into solid, liquid,or hybrid high energy propellant systems to improve the performancecharacteristics of such systems.

Other objects of the present invention will in part be obvious and willin part appear hereinafter.

It is known that the formation of a protective oxide coating on solid,high energy metals retards ignition of such metals until a much highertemperature is reached than would be required in the absence of such aprotective oxide.

It is known that when a protective oxide coating forms on the surface ofa solid metal being heated to ignition temperature in the presence ofoxygen or an oxygen containing environment, a temperature approaching orsubstantially equal to the melting point of the protective metal oxidecoating must be reached before ignition will occur. Since the meltingpoint of the protective oxide is usually substantially higher than theignition temperature of the base metal, it will readily be appreciatedthat the presence of the protective oxide considerably hampers theignition performance of the base metal.

According to this invention, it has been discovered that 3,328,805Patented June 27, 1967 formation of protective oxide coatings on metalsor particles thereof undergoing combustion may be avoided orsubstantially eliminated by amalgamating the surfaces of the metals ormetal particles prior to subjecting them to the combustion or ignitionenvironment.

Amalgamation of the metal surface may be readily accomplished bycontacting the metal or a surface portion thereof with mercury in theliquid or gaseous phase, or in the form of mercury salts or alloys, aswill be more fully described hereinbelow.

Amalgamation not only prevents the formation of a protective oxide layerbut also provides a surface amalgam which is generally more active thanthe pure metal itself, thereby further enhancing the ignition propertiesof the metal.

Because of the high activity of the surface amalgam, it will generallybe necessary to store the metal particles of this invention in inertenvironments which are free or substantially free of oxygen, e.g., undervacuum, in inert gases such as nitrogen, hydrogen, helium, argon, neon,krypton, and the like, or under inert liquids, such as hydrocarbons,e.g., hexane, or in non-reactive binders as in a solid propellant orhybrid fuel grain.

Although particularly directed to metal containing fuels or fuelsystems, this invention is generally useful whenever it is desired toburn or otherwise react metals to produce power, heat or light.

Thus, metals, e.g., magneisum or aluminum, treated in the mannerdescribed herein could be used to good advantage in camera flash bulbsand flares, as well as in other pyrotechnic display devices. The metalsor metal particles described herein could also be used in hightemperature cutting or welding torches, e.g., oxyacetylene torches. Insuch torches, the metal particles could be injected into the oxygenstream.

As a further and important application, metals treated in accordancewith the teachings contained herein may be used as components in theso-called metallized explosives, i.e., explosives in the nature ofdynamite comprising conventional oxidants, e.g., ammonium nitrate, andmetallic particles.

In all of these applications, it is the rapid, low temperature ignitionproperties of the solid metals of this invention which are exploited toenhance the operational performance and the efficiency of the devices orcompositions containing the metals as components.

Although theinvention will be particularly described in connection withthrust propellants, it should be understood that the basic concepts areequally applicable to other, more general applications of the typedescribed. 7

When metals which form protective oxide are heated in anoxygen-containing environment, a protective oxide coating forms andbuilds up as the temperature is raised to ignition. The protective metaloxide coating adversely affects the performance of the metal, since itresults in a longer ignition time and higher ignition temperature thanwould be required were the coating not present. In thrust propellantmotors utilizing metal containing fuels, the fuel has a relativelyshort, limited residence time in the combustion chamber of the engine.Protective oxide coatings which form on the metal components of suchpropellants cause delay in ignition time and high ignition temperatures,thereby leading to incomplete combustion and reduction in the deliveredperformance of the fuel.

The use of metals having amalgamated surfaces as fuel additives insolid, liquid, or hybrid thrust propellant systems will increase thedelivered performance through reduction in ignition delay, which willlead in turn to more complete combustion of the metal in the combustionchamber.

Further, hypergolicity of some bipropellant liquid rockets will beimproved or obtained by the addition of the activated (amalgamated)metal particles of this invention to the fuel phase of the propellants.

The invention is generally applicable to improve ignition performance ofall metals, including alloys, combinations or mixtures of metals, whichform an alloy with mercury, i.e., an amalgam.

Typical of the metals which do form amalgams and to which this inventionapplies are:

Beryllium Magnesium Aluminum Titanium Zirconium Chromium includingalloys or mixtures of the foregoing, and alloys or mixtures containingat least one of the foregoing metals. Particularly advantageous resultsare achieved when the invention is practiced with: aluminum; beryllium;alloys or mixtures of aluminum and beryllium; alloys or mixtures of anyof the listed metals with aluminum; alloys or mixtures of any of thelisted metals with beryllium; and alloys or mixtures of any of thelisted metal with lithium.

Aluminum and beryllium, including alloys or mixtures comprisingberyllium and aluminum, treated as described herein, constitutepreferred species of the invention. In this category may also bementioned alloys or mixtures of aluminum, beryllium, or mixtures ofaluminum and beryllium, with lithium.

The surfaces of the metals may be amalgamated in a variety of ways.

Thus, mercury could be added to a molten form of the metal or alloy, andthe resulting admixture solidified.

Alternatively, the metal or alloy may be contacted or otherwise treatedwith mercury in liquid (pure or alloy) or vapor form, or may be treatedwith appropriate aqueous or organic solutions of mercury salts, e.g.,mercury iodide, chloride, bromide, nitrate, bromate, chlorate,fulminate, and the like, to thereby form an alloy of the metal withmercury, i.e., an amalgam, at the surface of the metal or alloy.

It will be appreciated that the teachings contained herein areapplicable regardless of the form, shape, or size of the metal or alloybeing treated.

Typically, however, the metal or alloy will be in a form which willprovide a relatively high surface to volume ratio, such as a sphere,cylinder, torroid, and the like.

Ordinarily the metal or alloy will be in the form of spheres,irregularly shaped granules, wires, strips, and the like, which have, asan inherent characteristic, a minimum size in one direction, e.g., adiameter. As used herein, the term metal particle or particles isintended to encompass a wide variety of shapes, including spheres,irregularly shaped granules, wires, strips, slivers, chips, and thelike.

The burning efficiency of metals is a function of many variables. Forany given metal, however, the burning efficiency can be generally saidto vary inversely with the size of the particle sought to be burnedthelarger the particle-the lower the burning efficiency.

For rapid burning rate and high burning efficiency, the metal particlesshould possess, as an inherent characteristic, a small minimum dimensionin one direction, e.g., a diameter, so as to provide a large surface tovolume ratio.

One of the advantages of the present invention resides in the fact thatit permits utilization in thrust propellants of metal particles having aminimum dimension which is larger than has heretofore been generallypossible.

Heretofore in thrust propellant technology, metal particles with minimumdimensions of 0.010" to 0.025 were about the largest that could bepractically used, even with the biggest motors available, because of theproblems encountered with ignition of larger particles. With theamalgamated particles of this invention, use of metal particles having aminimum dimension of up to 1 or even larger is entirely possible,although the particles will ordinarily have a minimum dimension of up to/2".

Amalgamated metal particles of the type described having a minimumdimension ranging from about 0.001 micron to about A constitutepreferred embodiments of this invention.

Dimensions of the metal particles other than the minimum dimension arenot particularly significant. Thus, wires or strips having a minimumdimension as described supra and lengths of up to several miles or evenlonger are entirely within the purview of the invention and entirelyfeasible for use with the larger rocket engines.

Metallic particles having amalgamated surfaces will ignite more readilyin the combustion chamber of a rocket motor and therefore will achievemore complete combustion within the chamber, thereby leading to greaterdelivered performance. Since the amount of mercury required to producethe amalgamated surface is small, the presence of mercury will notreduce the potential impulse of the metal particles appreciably.

The nature of this invention will be made more clear by the followingexample.

Example A large number of runs were made to ascertain the ignitiontemperature of untreated vs. amalgamated aluminum wire.

The aluminum wires utilized were 99.99% pure and had a length of 4inches and a diameter of 500 microns.

Amalgamation was accomplished by placing a drop of dilute (5%) alcoholicmercuric chloride on the center of the wire. The wire was then subjectedto high vacuum to evaporate the alcohol. The wires treated in thismanner were maintained under vacuum until testing to prevent prematureoxidation.

The drawing is a graph of the results obtained from these tests.

In the drawing, the wire ignition temperature in degrees Kelvin (Deg K)is plotted as ordinate vs. pressure in pounds per square inch absolute(p.s.i.a.) as abscissa.

The shaded portion of the graph represents a band of over 60 data pointstaken with untreated, pure (99.99%) aluminum wire in a gas containing 30to percent oxygen. The width of the band gives an indication of thespread of the experimental data. In the horizontal portion of the shadedarea the coeflicient of variation is less than 1, corresponding to astandard deviation of :21 K.

The circles represent individual data points for the amalgamated wire.Amalgamation, as described above, was accomplished by treatment withdilute (5%) alcoholic mercuric chloride.

In the region below 10 p.s.i.a. there is no statistical significance toany differences between the treated and untreated wires. Above 10p.s.i.a., and therefore in the region of practical significance, thereis a statistically significant difference in the ignition temperature oftreated and untreated aluminum wire. From the graph it can be shown thatthe amalgamated aluminum wires have an ignition temperature on the orderof K. lower than the untreated wire.

As will be clear from the example and accompanying graph, theamalgamation treatment of this invention leads to a surprising reductionin ignition temperature of metal particles to be used as components inrocket propellants. This reduction in ignition temperature, asdescribed, supra, is immediately translatable into greater deliveredperformance when the amalgamated metal particles are utilized as acomponent in fuels, e.g., rocket propellants.

Metal treated in accordance with this invention can be used in the solidgrain of a hybrid or tripropellant rocket to provide improvedperformance. The binder or matrix material which holds the metalparticles in the grain will also serve to prevent reaction of theactivated surfaces in the atmosphere during storage.

Normal storage of the activated metal will however have to be under aninert atmosphere in order to prevent pre-ignition reaction.

Metal treated in the manner described may also be used in a slurry orgel of a non-oxidizing fluid in a bipropellant liquid rocket. In manycases hypergolicity will resultfrom the use of metals whose surfaceshave been activated by amalgamation.

Use of an amalgamated metal in solid rockets will also be advantageousbut in such formulations, some form of protection for the treated metalwill ordinarily be required to prevent reaction with the solid stateoxidizer during mixing, curing, or storage.

Besides the metal, rocket propellants will comprise an oxidizer orutilize an oxidizer as a component. By oxidizer is means oxygen or achemical capable of being decomposed to yield oxygen. When solid, thefuel will comprise a binder. Other constituents of rocket propellantsare well known in this art. Fuels, i.e., chemical substances capable ofchemically combining with oxygen to release heat, other than the metalcomponent may also be used. It hould be understood that the teachingscontained here are equally applicable to any thrust propellant systemwhich utilizes metal as a high energy additive.

Typical rocket propellant systems in which metals treated as describedherein can be used to good advantage are described in United StatesPatents Nos. 3,133,842 and 3,112,609.

The invention in its broader aspects is not limited to the specificdetails shown and described but departures may be made therefrom withinthe scope of the accompanying claims without departing from theprinciples of the invention and without sacrificing its chiefadvantages.

What is claimed is:

1. In a method of operating a thrust propellant motor, wherein fuelcomprising metal as a component is burned in a combustion chamber andthe products of combustion are allowed to escape through a jet, therebyproducing a driving force, the improvement which comprises utilizing, ametal selected from the group consisting of beryllium, aluminum,zirconium, magnesium, titanium, chromium, mixtures and alloys of theforegoing and mixtures and alloys containing at least one of theforegoing, said metal having a surface coating which is an amalgam ofsaid metal, characterized by an ignition temperature which is lower thanthe ignition temperature of said metal itself.

2. The method of claim 1 wherein the fuel comprises, in addition to saidmetal, an organic binder.

3. The method of claim 1 wherein the fuel comprises, in addition to aidmetal, an oxidizer.

4. The method of claim 1 wherein the fuel comprises, in intimateadmixture with said metal, an oxidizer and an organic binder.

5. A method for producing power which comprises reacting with anoxidizer a metal selected from the group consisting of beryllium,aluminum, zirconium, magnesium, titanium, chromium, mixtures and alloysof the foregoing, and mixtures and alloys containing at least one of theforegoing, the surface of said metal having a coating which is anamalgam of said metal characterized by an ignition temperature which islower than the ignition temperature normally associated with the metalitself.

6. The method of producing power which comprises contacting aluminummetal with an oxidizer, the surface of said aluminum metal having acoating which is an amalgam of aluminum having an ignition temperaturewhich is substantially lower than the ignition temperature of aluminummetal.

7. In a method for preparing a fuel composition containing a high energymetal selected from the group consisting of beryllium, aluminum,zirconium, magnesium, titanium, chromium, mixtures and alloys of theforegoing and mixtures and alloys containing at least one of theforegoing the improvement which comprises contacting the metal with amember selected from the group consisting of mercury and salts ofmercury under conditions such that an amalgam of said metal,characterized by an ignition temperature which is lower than theignition temperature of said metal itself, forms as a coating on thesurface of said metal.

8. The improvement of claim 7 wherein said metal comprises lithium as acomponent.

9. A high energy fuel system comprising, as a component, a metalselected from the group consisting of beryllium, aluminum, zirconium,magnesium, titanium, chromium, including mixtures and alloys of theforegoing, and mixture and alloys containing at least one of theforegoing, said metal having a surface coating which is an amalgam ofsaid metal characterized by an ignition temperature which is lower thanthe ignition temperature of said metal itself.

10. The system of claim 9 wherein said member is aluminum.

11. The system of claim 9 wherein said member is an alloy of berylliumand aluminum.

12. The system of claim 9 wherein said member is an alloy of aluminumwith a member selected from the group consisting of beryllium,magnesium, zirconium, titanium, silicon, chromium, lithium and mixturesof the foregoing.

13. The system of claim 9 wherein said member is an alloy of berylliumwith a member selected from the group consisting of aluminum, zirconium,magnesium, silicon, titanium, chromium, lithium, and mixtures of theforegoing.

14. The high energy fuel system of claim 9 wherein said metal compriseslithium as a component.

15. As a new article of manufacture, a metal selected from the groupconsisting of beryllium, aluminum, zirconium, magnesium, titanium,chromium, including mixtures and alloys of the foregoing, and mixturesand alloys containing one of the foregoing, said metal having a surfacecoating which is an amalgam of said metal, characterized by an ignitiontemperature which is lower than the ignition temperature of the metalitself, said metal having a shape which includes a minimum dimensionwhich is less than about 1 inch.

16. The metal particle of claim 15 wherein the metal comprises lithiumas a component.

17. An article in accordance with claim 15, wherein said metal has ashape which includes a minimum dimension which ranges between about0.001 micron and inch.

18. The system of claim 9, wherein said member is beryllium.

References Cited UNITED STATES PATENTS 385,309 6/1888 Hewett et al.117-131 3,006,745 10/1961 Toulmin 14944 3,151,009 9/1964 Toulmin 149-33L. DEWAYNE RUTLEDGE, Primary Examiner.

BENJAMIN R. PADGETT, Examiner.

S. I. LECHERT, JR., Assistant Examiner.

1. IN A METHOD OF OPERATING A THRUST PROPELLANT MOTOR, WHEREIN FUELCOMPRISING METAL AS A COMPONENT IS BURNED IN A COMBUSTION CHAMBER ANDTHE PRODUCTS OF COMBUSTION ARE ALLOWED TO ESCAPE THROUGH A JET, THEREBYPRODUCING A DRIVING FORCE, THE IMPROVEMENT WHICH COMPRISES UTILIZING, AMETAL SELECTED FROM THE GROUP CONSISTING OF BERYLLIUM, ALUMINUM,ZIRCONIUM, MAGNESIUM, TITANIUM, CHROMIUM, MIXTURES AND ALLOYS OF THEFOREGOING AND MIXTURES AND ALLOYS CONTAINING AT LEAST ONE OF THEFOREGOING, SAID METAL HAVING A SURFACE COATING WHICH IS AN AMALGAM OFSAID METAL, CHARACTERIZED BY AN IGNITION TEMPERATURE WHICH IS LOWER THANTHE IGNITION TEMPERATURE OF SAID METAL ITSELF.
 7. IN A METHOD FORPREPARING A FUEL COMPOSITION CONTAINING A HIGH ENERGY METAL SELECTEDFROM THE GROUP CONSISTING OF BERYLLIUM, ALUMINUM, ZIRCONIUM, MAGNESIUM,TITANIUM, CHROMIUM, MIXTURES AND ALLOYS OF THE FOREGOING AND MIXTURESAND ALLOYS CONTAINING AT LEAST ONE OF THE FOREGOING THE IMPROVEMENTWHICH COMPRISES CONTACTING THE METAL WITH A MEMBER SELECTED FROM THEGROUP CONSISTING OF MERCURY AND SALTS OF MERCURY UNDER CONDITIONS SUCHTHAT AN AMALGAM OF SAID METAL, CHARACTERIZED BY AN IGNITION TEMPERATUREWHICH IS LOWER THAN THE IGNITION TEMPERATURE OF SAID METAL ITSELF, FORMSAS A COATING ON THE SURFACE OF SAID METAL.
 9. A HIGH ENERGY FUEL SYSTEMCOMPRISING, AS A COMPONENT, A METAL SELECTED FROM THE GROUP CONSISTINGOF BERYLLIUM, ALUMINUM, ZIRCONIUM, MAGNESIUM, TITANIUM, CHROMIUM,INCLUDING MIXTURES AND ALLOYS OF THE FOREGOING, AND MIXTURES AND ALLOYSCONTAINING AT LEAST ONE OF THE FOREGOING, SAID METAL HAVING A SURFACECOATING WHICH IS AN AMALGAM OF SAID METAL CHARACTERIZED BY AN IGNITIONTEMPERATURE WHICH IS LOWER THAN THE IGNITION TEMPERATURE OF SAID METALITSELF.
 15. AS A NEW ARTICLE OF MANUFACTURE, A METAL SELECTED FROM THEGROUP CONSISTING OF BERYLLIUM, ALUMINUM, ZIRCONIUM, MAGNESIUM, TITANIUM,CHROMIUM, INCLUDING MIXTURES AND ALLOYS OF THE FOREGOING, AND MIXTURESAND ALLOYS CONTAINING ONE OF THE FOREGOING, SAID METAL HAVING A SURFACECOATING WHICH IS AN AMALGAM OF SAID METAL, CHARACTERIZED BY AN IGNITIONTEMPERATURE WHICH IS LOWER THAN THE IGNITION TEMPERATURE OF THE METALITSELF, SAID METAL HAVING A SHAPE WHICH INCLUDES A MINIMUM DIMENSIONWHICH IS LESS THAN ABOUT 1 INCH.